The present invention relates to power supplies, and more particularly, to an improved power supply for use in powering linear accelerators, and similar devices.
Linear accelerators are used in a wide variety of applications. One important application is use in radiation therapy devices for the treatment of patients. In such an application, the linear accelerator is used to generate a high energy radiation beam for therapy. The high energy radiation beam is directed at a treatment zone (such as a cancerous tumor) on a patient to provide a selected dose of therapeutic radiation pursuant to a treatment plan prescribed by, e.g., an oncologist.
Typically, electron guns are used to generate electron beams supplied to the linear accelerator. A high energy beam is then created using a high frequency source (such as a magnetron or klystron) to supply radio frequency signals for the generation of an electromagnetic field. This electromagnetic field accelerates electrons in the accelerator, creating a high energy beam. The high energy beam can be an electron or photon (X-ray) beam.
An important component of these radiation therapy devices is the power system which drives the electron gun and the high frequency sources. Typically, a radiation therapy device may have one or more power systems, one to provide power to drive the electronic gun and one to provide high frequency power to drive either a magnetron, klystron, or other high frequency source. There is typically a different design for each power system, and often a different design is used for different high frequency sources. These power systems are used in an extremely unforgiving environment requiring high accuracy, reliability, maintainability and safety in a relatively small footprint all at a low cost of operation.
Highly accurate power supplies, delivering accurate pulsed power at a prescribed frequency are needed. Treatment therapies, typically prescribed for each patient by an oncologist, require accurate delivery of prescribed doses of therapeutic radiation. Accurate control of the power system driving the magnetron, klystron, and/or electron gun is essential to this accurate delivery of radiation.
The overall reliability of radiation therapy devices is an important concern to users of the devices and to patients. Typically, radiation therapy devices are very expensive units operated by hospitals and treatment centers (generically referred to herein simply as xe2x80x9chospitalsxe2x80x9d) to treat life-threatening ailments such as cancer. Hospitals often can only afford one or two radiation therapy devices and therefore demand very high reliability in their operation. Because of their high cost, hospitals often run these devices at a brisk pace, scheduling treatments throughout every working hour of the week. Failure of the device is potentially devastating to both the hospital (in terms of revenue, scheduling, and patient care) as well as to patients who have a real and pressing need for uninterrupted treatment.
There is also a need for radiation therapy devices which are easily maintained. Electronic components do not last forever. Eventually, components require maintenance and/or replacement. When maintenance or replacement is required it is desirable to provide components which are easily and quickly maintained and installed by relatively unskilled workers.
The environment for these radiation therapy devices is made even more difficult due to space and power consumption constraints imposed by hospitals. Many hospitals can only install radiation therapy devices which occupy a relatively small amount of space. Other hospitals require several radiation therapy devices to satisfy the treatment needs of their patients, but can only install several devices if each of their footprints is small.
Existing power systems for linear accelerators in radiation therapy devices do not necessarily meet these needs for high accuracy, reliability, maintainability, and safety in a small footprint and at a low cost of operation. Many existing power systems for linear accelerators are large, heavy devices that significantly increase the cost and size of the radiation therapy system. One typical power system utilizes a high voltage transformer/rectifier system to generate a 21 kV DC power source from a conventional three-phase 208 V power source. The high voltage DC source is then used to generate a 15 kV pulse that is converted to the required 150 kV pulse via a high voltage pulse transformer. The high voltage transformer/rectifier assembly typically weighs 500 lbs. and occupies eight cubic feet. As a result, the power supply must be housed in a separate cabinet from the linear accelerator. In addition to increasing the floor space needed to house the accelerator system, this additional cabinet requires special power transmission lines to couple the klystron output to the linear accelerator which further increases the cost and complexity of the system. Finally, the sheer weight of the system increases the cost of shipping.
Many existing power systems utilize a pulse forming network and a switch tube known as hydrogen thyratron. A thyratron is a low pressure gas device with a thermionic cathode. Over time, the cathode depletes itself. Thus, a thyratron has an inherent wear out mechanism. More recently, solid state power systems have been proposed. However, many of these systems utilize semiconductor controlled rectifiers (SCRs) to modulate the high voltage pulses needed to drive klystrons or magnetrons. Current SCRs tend to wear out relatively quickly under these conditions.
It would be advantageous to provide a method and apparatus that overcame the drawbacks of the prior art. In particular, it would be desirable to provide a solid state power architecture with greater reliability and maintainability which provides highly accurate pulsed power to a variety of different loads. Preferably, the power architecture achieves fast output pulse rise times in a modular architecture in a cost effective package taking up relatively little space.
To alleviate the problems inherent in the prior art, embodiments of the present invention provide a unified power architecture suitable for powering devices requiring high voltage pulsed power, such as klystrons, magnetrons, or the like.
In one embodiment of the present invention, a unified power architecture for generating high frequency switched power to a load is provided which includes a number of input branches, each input branch receiving direct current (DC) power from a power source. Each input branch includes a switch device coupled to a storage device for generating input pulses, and a transformer including a primary winding set receiving the input pulses. An output section is provided which includes a secondary winding set around a secondary of each transformer of each of the input branches, the output section generating an output pulse including components of each of the input pulses.
According to one embodiment of the present invention, the output pulse is provided to a droop compensation circuit which ensures that the output pulse is of a good quality shape.
According to another embodiment of the present invention, the number of input branches is selected based on the requirements of the load to be driven. In one embodiment, two input branches are provided to drive a magnetron, while five input branches are provided to drive a klystron. In one embodiment, portions of each input branch is formed on a separate printed circuit board (PCB). In one embodiment, each input branch is interchangeable. The result is a unified power supply which is highly reliable, easily maintained, modular, accurate, all with a low cost of operation in a small footprint.
In one embodiment, the switch of each input branch is performed using an Insulated Gate Bipolar Transistor (IGBT) operatively controlled by a control device.
With these and other advantages and features of the invention that will become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims and to the several drawings attached herein.